AT7382U1 - HEAT SINK WITH HIGH HEAT-CONDUCTIVITY - Google Patents

Abstract

The invention relates to a component as a heat sink made of a diamond-containing composite material. In addition to a diamond content of 40-90% by volume, the composite material contains 0.1 to 12% by volume of silicon carbide, 7 to 49% by volume of an Ag, Au or Al-rich phase and less than 5% by volume of a further phase. wherein the volume ratio of the Ag, Au or Al-rich phase to silicon carbide is greater than 4 and the diamond grains are coated to at least 60% of their surface area of silicon carbide. Preferred manufacturing methods include pressureless and pressure assisted infiltration techniques. The component is particularly suitable as a heat sink for semiconductor components.

Description

AT 007 382 U1

The invention relates to a component as a heat sink made from a composite material with a diamond content of 40-90% by volume, with a mean diameter of the diamond grains of 5 to 300 μm, and to a process for its production.

Heat sinks are widely used in the manufacture of electronic components. In addition to the heat sink, the semiconductor component and a mechanically stable enclosure are the essential components of an electronic package. For the heat sink, the terms substrate, heat spreader or carrier plate are also often used. The semiconductor component consists for example of monocrystalline silicon or gallium arsenide. This is connected to the heat sink, wherein as fügetechnik usually Lötverfäh-10 ren are used. The heat sink has the function to dissipate the heat generated during operation of the semiconductor component. Semiconductor components with particularly high heat generation are, for example, laterally diffused metal oxide semi-conductor (LDMOS), laser diodes, central processing unit (CPU), microprocessor unit (MPU) or high frequency amplify device (HFAD). 15 The geometric designs of the heat sink are application-specific and diverse. Simple shapes are flat platelets. However, complex substrates with recesses and steps are also used. The heat sink itself in turn is connected to a mechanical stable enclosure.

The coefficients of thermal expansion of the semi-conductor materials used are low compared to other materials and are reported in the literature for silicon with 2.1 x 10 ** IC1 to 4.1 x KT6 IC1 and for gallium arsenide 5.6 x 10 "6 IC1 to 5.8 x 10 * IC1 indicated.

Also other semiconductor materials that are not widely used on a large scale, such as. Ge, In, Ga, As, P or silicon carbide have similarly low coefficients of expansion. For the cladding usually ceramic materials, composite materials or 25 plastics are used. Examples of ceramic materials are Al 2 O 3 with a coefficient of expansion of 6.5 × 10 -6 "-1 or aluminum nitride with an expansion coefficient of 4.5 × icrV.

If the expansion behavior of the components involved is different, stresses are built into the composite which can lead to distortions, detachment or breakage of the components. Tensions can already arise during the manufacture of the package during the cooling phase from the soldering temperature to room temperature. However, even during operation of the package, temperature fluctuations occur, ranging for example from -50 ° C to 200 ° C and can lead to thermo-mechanical stresses in the package.

This results in the requirements for the material for the heat sink. On the one hand, it should have as high a thermal conductivity as possible in order to keep the temperature rise of the semiconductor component during operation as low as possible. On the other hand, it is necessary for the thermal expansion coefficient to be adapted as well as possible to both the semiconductor component and to the shell. Single-phase metallic materials do not sufficiently fulfill the required property profile, since the materials with high thermal conductivity also have a high coefficient of thermal expansion.

Therefore, in order to meet the requirement profile, composites or composite materials are used for the production of the substrate. Conventional tungsten-copper and Mo-copper composite materials or material composites as described for example in EP 0 100 232, US Pat. No. 4,950,554 and US Pat. No. 5,493,153 have a thermal conductivity at room temperature of from 170 to 250 W / (mK). at a coefficient of thermal expansion of 6.5 xlff6 to 9.0 x 10 " 6 K " 1, which is insufficient for many applications.

With the increasing demands on the thermal conductivity of heat sinks, diamond or diamond-containing composites or composite materials would also be of interest. Thus, the thermal conductivity of diamond lies at 1,000 to 2,000 W / (m.K), whereby the content of nitrogen and boron atoms on lattice sites is the determining factor in quality.

EP 0 521 405 describes a heat sink which has a polycrystalline diamond layer on the side facing the semiconductor chip. Due to the lack of plastic deformability of the diamond layer, cracks in the diamond layer may already occur during cooling of the coating temperature. 2 AT 007 382 U1

US 5,273,790 describes a diamond composite having a thermal conductivity > 1,700 W / (m.K), in which loose, shaped diamond particles are transferred by means of subsequent diamond deposition from the gas phase into a stable shaped body. The diamond composite produced in this way is too expensive for commercial use in parts by mass. In WO 99/12866 a method for producing a diamond-silicon carbide composite is described. The production takes place by infiltration of a diamond skeleton with silicon or a silicon alloy. Due to the high melting point of silicon and the resulting high infiltration temperature diamond is partially converted into carbon or subsequently into silicon carbide. Due to the high brittleness, the mechanical machinability of this material is highly problematic and expensive, so that this composite material has not hitherto been used for heat sinks.

US Pat. No. 5,045,972 describes a composite material in which apart from diamond particles with a size of 1 to 50 μm there is a metallic matrix consisting of aluminum, magnesium, copper, silver or their alloys. The disadvantage here is that the metallic matrix is only connected to the diamond in a manner which makes the thermal conductivity and mechanical integrity inadequate.

Also, the use of finer diamond powder, for example, with a grain size < 3 pm, as disclosed in US 5,008,737, does not improve diamond / metal adhesion.

EP 0 859 408 describes a material for heat sinks whose matrix of diamond particles and metal carbides is formed, wherein the interspaces of the matrix are filled by a metal. The metal carbides are the carbides of the metals of 4a to 6a groups of the periodic table. Particular emphasis is given in EP 0 859 408 to TiC, ZrC and HfC. Particularly advantageous filler metals are Ag, Cu, Au and Al. The disadvantage is that the metal carbides have a low thermal conductivity, which is in the range of 10 to 65 W / (m.K) for TiC, ZrC, HfC, VC, NbC 25 and TaC. Furthermore, it is disadvantageous that the metals of 4a to 6a groups of the periodic table have a solubility in the filler metal, such as silver, whereby the thermal conductivity of the metal phase is greatly reduced.

In recent years, the process speed and the degree of integration of the semiconductor components has greatly increased, which has also led to an increase in the heat development in the package 30. An optimal thermal management is therefore an increasingly important criterion. The thermal conductivity of the materials described above is no longer sufficient for a variety of applications, or their production is too expensive for wide use. The availability of improved, low cost heat sinks is a prerequisite for further optimization of semiconductor devices. Thus, it is an object of the present invention to provide for a heat sink component a composite having high thermal conductivity and a low coefficient of expansion in processing characteristics allow a cost-effective production.

This object is achieved by a component made of a diamond-containing composite comprising 40 0.1 to 12 vol.% Of silicon carbide, 7 to 49 vol.% Of an Ag, Au or Al-rich phase and < 5 vol.% Of another phase, wherein the volume ratio of the Ag, Au or Al-rich phase to silicon carbide is greater than 4 and the Diamantkömer are coated to at least 60% of its surface of silicon carbide.

The component of the present invention has excellent adhesive strength between the diamond grains and the Ag, Au or Al-rich phase through the silicon carbide formed therebetween. In contrast to the metal carbides, silicon carbide has a very high thermal conductivity of about 250 W / (m.K). Since the solubility of Si in Ag, Au and Al is very low at room temperature, the very high thermal conductivity of these metals in the pure state is only slightly deteriorated. Furthermore, the mechanical workability due to the very ductile Ag, so Au or Al structural components is given to a sufficient extent. For a cost-effective representation, it is also advantageous that the diamond content can be reduced by the high thermal conductivity of the Ag, Au or Al-rich microstructural constituents. By varying the diamond, silicon carbide and metal phase content, it is possible to produce tailor-made heat sinks for a wide variety of requirements with regard to thermal conductivity and thermal expansion. 3 AT 007 382 U1

Further structural test contents do not impair the properties to an unacceptable extent as long as their content does not exceed 5% by volume. These include unbound silicon and unbound carbon. Although these microstructural constituents slightly impair the thermal conductivity, they have a favorable effect on the thermal expansion coefficient 5, by reducing it. In addition, they can partially be completely avoided in terms of manufacturing technology only with relatively great effort.

Particularly advantageous contents of silicon carbide and Ag, Au or Al-rich phase are from 0.2 to 7 vol.% And at 7 to 30 vol.%. Experiments have shown that diamond powders can be processed in a wide range of grain sizes. In addition to natural diamonds can also be processed 10 cheaper synthetic diamonds. Even with the common coated diamonds excellent processing results were achieved. It follows that the most cost-effective grade can be used, for cost-critical applications with extremely high requirements for thermal conductivity, it is advantageous to use a diamond fraction having a mean grain size in the range of 50 to 150 pm. Furthermore, the highest thermal conductivity values can be achieved by using Ag at levels of 7 to 30% by volume. For the production of various methods can be used. So it is possible to compact silicon carbide coated diamond powder with Ag, Au or AI under temperature and pressure. This can be done for example in hot pressing or hot isostatic pressing. The infiltration has been shown to be particularly advantageous. In this case, a precursor or precursor is prepared which contains not only diamond powder but also a binder. Particularly advantageous are binders which pyrolyze to a high degree under the influence of temperature. Advantageous binder contents are from 1 to 20% by weight. Diamond powders and binders are mixed in conventional mixers or mills. Thereafter, the shaping takes place, whereby this can be done by pouring into a mold or pressure assisted by pressing or metal powder injection molding. Subsequently, the precursor is heated to a temperature at which the binder at least partially pyrolyzed. However, the pyrolysis of the binder can also take place during the heating during the infiltration process. The infiltration process can be pressureless or pressure assisted. The latter is commonly referred to as squezze casting. As the infiltrating material, a film of Ag-Si, Au-Si or Al-Si alloy having an Si content of < 50% by weight used. For the choice of the composition is to be considered that the liquidus temperature of the respective alloy is advantageously not higher than 1200eC, otherwise decompose too high diamond shares. Films with a eutectic composition are particularly suitable for infiltration. In addition to the particularly advantageous use of the components for heat dissipation in semiconductor components of the composite material according to the invention can also be used as a heat sink in other applications such as in the field of aerospace or engine construction.

In the following the invention is explained in more detail by manufacturing examples. 40

example 1

Natural diamond powder of quality HA (Micron + SND der-Element Six GmbH) with a mean grain fraction of 40 - 80 pm was mixed with 7 volume percent of an epoxy resin-based binder. The precursor or precursor thus produced was pressed by means of die pressing at a pressure of 200 MPa to a plate of dimension 35 mm × 35 mm × 5 mm. The pore content of the plate was about 15 vol.%. Subsequently, this plate was covered with a sheet of eutectic Ag-Si alloy, wherein the Si content was 11 at% and heated to a temperature of 860 ° C in a vacuum oven to be infiltrated, the holding time being 15 minutes amounted to. After cooling to room temperature with a breakpoint at 400 ° C for approx. 50 10 minutes, the volume contents of the existing phases was determined by quantitative metallography.

The value of silicon carbide was about 2 vol.%, The silicon carbide largely covers the diamond grains evenly. Due to the low layer thickness of this silicon carbide cladding, the modification of the silicon carbide phase could not be determined. In addition to diamond 55 and silicon carbide, the microstructure consists of an Ag-rich phase with intercalated 4

Claims (11)

AT 007 382 U1 Si precipitates formed by the eutectic reaction. The volume fraction of the Ag-rich phase was about 12%, that of Si about 1%. By means of EDX, no further constituents could be detected in the Ag-rich phase in addition to Ag, so that based on the given detection limit it can be assumed that the Ag content is greater than 5 99 atom%. To determine the thermal conductivity and the thermal expansion coefficient of the plate was processed by laser and erosion. For the thermal conductivity at room temperature, a mean value of 450 W / (m.K) was measured. The determination of the coefficient of thermal expansion yielded a mean value of 8.510 " 6 IC1 2 3 4 5 6. 10 Example 2 In a further experiment, synthetic diamond powder of Micron + MDA grade from Element Six GmbH and an average 40-80 μm fraction was processed. The processing was carried out as described in Example 1. The average thermal conductivity at room temperature of the composite produced in this way was 410 W / (m.K), the average thermal expansion coefficient 9.0 10-IC1. Example 3 In a further experiment, synthetic diamond powder of the quality Micron + MDA from 20 Element Six GmbH was processed with an average fraction of 40-80 μm. The precursor preparation was carried out as described in Example 1. The infiltration of the pressed precursor with a eutectic Ag-Si melt was carried out in a conventional squeeze-casting apparatus whose hot-work tool mold was preheated to 150 ° C at a gas pressure of about 40 MPa. The temperature of the Ag-Si melt was about 880 ° C. The following, slow cooling to room temperature was carried out with a breakpoint at 400 ° C for about 15 minutes. The average thermal conductivity at room temperature of the composite thus prepared was 480 W / (m.K), the average coefficient of thermal expansion 8.5 10 "IC1. Example 4 Synthetic diamond powder of the Micron - * - MDA quality of Element Six GmbH having a terry grain fraction of 40-80 μm was processed in accordance with Example 3, but without a holding phase being carried out at approximately 400 ° C. for 15 minutes on cooling from the infiltration temperature has been. The average thermal conductivity at room temperature of the composite thus prepared was 440 W / (m.K), the average coefficient of thermal expansion 8.5 ppm / K. 35 REQUIREMENTS: 40 45 50 5 55 1 Component as heat sink consisting of a composite material with a diamond content of 50 to 90% by volume with a mean size of the diamond grains of 5 to 300 μm; characterized in that the composite material contains 0.1 to 12% by volume of silicon carbide, 7 to 49% by volume of an Ag, Au or Al-rich phase and less than 5% by volume of a further phase, the volume ratio of the , Au or Al-rich phase to silicon carbide is greater than 4 and the Diamantkömer are coated to at least 60% of its surface of silicon carbide. 2 component according to claim 1, characterized in that the Ag, Au or Al-rich phase contains at least 95 atomic percent of the respective element. 3 component according to claim 1 and 2, characterized in that the composite material contains 0.1 to 5 vol.% Unbound silicon. 4 component according to claim 1 to 3, characterized in that the composite material contains 0.1 to 5 vol.% Unbound carbon. 5 component according to claim 1 to 4, characterized in that the composite material contains 0.2 to 7 vol.% Silicon carbide and 7 to 30 vol.% Ag, Au or Al-rich phase. 6 component according to claim 1 to 5, characterized in that the diamond grain size is 50 to 150 pm. 5 10 15 20 25 30 35 AT 007 382 U1 7. Component according to claim 1 to 6, characterized in that the composite material contains 0.2 to 7 vol.% Silicon Carbide and 7 to 30 vol.% Ag. 8. A method for producing a component according to claim 1 to 7, characterized in that the method comprises at least the following process steps: - producing an intermediate substance containing diamond grains having a particle size of 5 to 300 pm and a binder based on polymer or wax, wherein the proportion of binder is from 1 to 20% by weight - shaping of the precursor by pressureless or pressure-assisted filling of a mold - producing a porous diamond body by scribing the precursor at 300 ° C. to 1200 ° C. under inert gas atmosphere for at least partial pyrolysis of the binder Process step may be integrated into the infiltration process - infiltration of the porous diamond body by heating it and a silicon-containing Ag, Au or Al alloy whose Si content at < 40 wt.% Is, to a temperature above the liquidus temperature of the respective silicon-containing Ag, Au or Al alloy, preferably in vacuum, wherein silicon reacts with both the carbon of the pyrolyzed binder, as well as with diamond at least partially to silicon carbide. 9. A method for producing a heat sink according to claim 1 to 7, characterized in that the method comprises at least the following process steps: - producing an intermediate substance containing Diamantkömer with a particle size of S to 300 pm and a binder based on polymer or wax, wherein the proportion of binder is from 1 to 20% by weight. - Forming the precursor by pressureless or pressure-assisted filling of a mold. - Producing a porous diamond body by heating the precursor to 300 ° C. to 1,200 ° C. under inert gas atmosphere for at least partial pyrolysis of the binder Process step may be integrated into the pressure infiltration process - heating a silicon-containing Ag, Au or Al alloy whose Si content at < 40% by weight, to a temperature above the liquidus temperature of the respective silicon-containing Ag, Au or Al alloy and pressure infiltration of the porous diamond body. 10. The method according to claim 9 or 10, characterized in that a eutectic Ag-Si alloy is used for infiltration. 11. Use of a component according to claim 1 to 10 as a heat sink for semiconductor components. NO DRAWING 40 45 50 6 55